The increase of the incidence of malformation of the genital tract and hormone-related cancers is a main health problem in the industrialized world. Environmental estrogens are suspected to be the casual agent. The long- term goal of this proposal is to understand the mechanisms underlying the toxicity of the environmental estrogen Bisphenol-A (BPA) on the female reproductive system and mammary gland. During the first period of funding, we found evidence that perinatal exposure to low- environmentally relevant doses of BPA produces irreversible alterations in the structure and function of estrogen-target tissues in female rodents. Increased body weight, changes in morphology of the ovary, uterus and mammary gland, and alterations in pattern of estrus cyclicity suggested that perinatal exposure to BPA may decrease reproductive success, and increase the risk of mammary gland cancer. Given the similarity of toxic effects of the synthetic estrogen diethylstilbestrol in rodents and humans, our results raise concern the exposure to BPA may put human health at risk. The overall hypothesis to be tested is that perinatal exposure to BPA results in morphological and functional alterations of the hypothalamus and/or pituitary as well as estrogen sensitive peripheral organs (i.e. mammary gland) by an ER-mediated process. These effects of BPA in development would in turn result in an altered response to ovarian and pituitary hormones in adulthood. The following complementary Specific Aims are proposed: Aim1: To assess the hypothesis that perinatal exposure to BPA alters a) sexual differential of the brain and b) the functionality of the circuitry involved in the luteinizing hormone and prolactin surges thus altering permanently the hormonal milieu of peripheral organs (i.e. mammary gland). Aim 2: To assess the hypothesis that in utero exposure to BPA directly affects the prenatal development of the mammary gland anlage by altering the expression of ER and downstream homeobox genes Msx2, Wnt10b). Aim 3: To assess the hypothesis that the morphological changes observed in the mammary glands are due to an altered response to gonadal and pituitary hormones. The responsiveness to various sex hormones will be assessed in ovariectomized mice following in utero exposure to BPA. The following techniques will be used: immunocytochemistry, in sit hybridization, quantitative PCR, morphometry, radioimmunoassays. The information obtained from these studies will considerably advance our understanding of the mechanisms underlying the developmental and reproductive toxicity of BPA. These data are needed to develop biomarkers and research strategies to apply these data to assess the toxic impact of xenoestrogens on human development and reproduction.